Rebalance servo control system



Oct. 12, 1965 E. w. BUTTENHOFF ETAL 3,211,977

REBALANCE SERVO CONTROL SYSTEM Filed April 15, 1963 MOTOR OVER RIDE CONTROL N I 38 DISCRIMINATOR, I

AMPLIFIER AND 14 POWER SUPPLY i I 6! J 52 REVERSIBLE MOTOR 107 INVENTCRS r. [DMPD WBl/TTENHOF/j I3 4 BY STA/VLEV S. H/vr/aH WM- V United States Patent 3,211,977 REBALANCE SERVO CONTROL SYSTEM Edward W. Buttenholr, Excelsior, and Stanley S. Kintigh, Hopkins, Minn., assignors to Honeywell Inc., a corpo ration of Delaware Filed Apr. 15, 1963, Ser. No. 272,945 9 Claims. (Cl. 318-29) The present invention relates generally to a motor control system in which the normal control is overridden by a second control under certain circumstances to obtain a more desirable function. More particularly, the present invention is directed to a call ofiice conveyor system wherein the conveyor is made to operate in its shortest route to deliver a particular point on the conveyor to a fixed location.

In recent years, many businesses have started to use motorized conveyor systems for delivery of material to fixed points. This is in industries other than manufacturing industries where conveyors have been in use for many years. The more common type of industry that has been utilizing this type of conveyor is the dry cleaning business. The dry cleaning industry has used motorized conveyors to deliver garments to a customer counter at the front or customer area of a store from any point on the conveyor. This type of conveyor system is generally referred to as a call ofiice conveyor. For the sake of convenience, the control system will be described in the present invention as utilized in a dry cleaning establishment so that the preferred embodiment can be readily understood. In dry cleaning establishments, long conveyors are utilized to hang finished garments for delivery to the customers as the customer calls for his freshly cleaned garments. The normal procedure is for the customer to approach a cash register area and present a slip or receipt indicating the particular work or garments that have been left for cleaning. The clerk then obtains a filed copy of the receipt which has an indication on it at which point on a long conveyor the particular garment has been placed. The positions on the conveyor are normally numerically indicated, and the number of the location of the garment is placed on the receipt retained on file at the cash register of the dry cleaning establishment. Once the number or location of the garment is ascertained by the clerk, the clerk activates a switch which energizes the drive motor for the conveyor, and the conveyor rotates until the numbered position desired comes within reach.

In the original call oifice conveyor systems, the conveyor was normally driven by a reversible motor which was in turn manually operated to give clockwise or counterclockwise revolutions of the conveyor. The clerk normally would note the position available at the time the garment was to be picked up and would mentally determine whether the conveyor should drive clockwise or counterclockwise to deliver the newly required number to the clerks position. The manual operation of a switch causing the motor to operate in a clockwise or counterclockwise direction required that the clerk continuously attend the conveyor until the desired garment was within reach. The system was then manually shut down and the garment delivered to the customer upon payment of the cleaning fee.

It became desirable to free the clerk of the job of waiting for the conveyor to deliver the proper garment and, more recently, call ofiice conveyor systems have been developedv that utilize a rebalance bridge servo control system with a potentiometer of the round-and-round type driven by the conveyor. One complete revolution of the potentiometer corresponds to one complete revolution of the conveyor. As such, it a conveyor is considered in degrees of rotation, it could be readily broken up into 360 positions to correspond to degrees of revolution of the potentiometer. This potentiometer was then connected into a bridge circuit with a corresponding potentiometer at the cash register or counter in the dry cleaning establishment. The system then required that the operator adjust the potentiometer at the cash register, which potentiometer had been calibrated in numbers corresponding to the numbers on the conveyor, and merely activating the system brought the proper number around on the conveyor. This type of system, however, has one major drawback. In order for the rebalance servo bridge control to operate, the potentiometer on the conveyor cannot be driven across its open or discontinuous section. With this requirement, the conveyor always operates in a direction to balance the system without driving the wiper across the open section. This meant that in some cases the conveyor would operate in a direction that would require the conveyor to make more than one-half of a complete revolution. In some cases, the conveyor systems under certain circumstances, would rotate in a direction that would require the conveyor to operate almost through the full 360 before the proper balance position was located.

More recently, a control system for this type of bridge balance servo system has been marketed which utilizes a sensing system that determines the shortest route for the conveyor to operate and in turn operates the conveyor in that direction. This type of system utilizes a bridge balance servo amplifier, but the amplifier can be reversed in its output by a relay or similar control device that is placed in parallel with the servo amplifier. Upon an unbalance of the bridge in excess of 50% of the voltage applied to the bridge, the relay would operate and the servo motor would turn on the drive motor. This would cause the system to operate in a reverse direction to which the bridge was normally adjusted and would drive the system to balance over the shortest route even though the potentiometer wiper had to be driven across the discontinuous section. At the time the motor drives the potentiometer across the open section, the servo amplifier reverses sense, but this reverse sense is not fed into the motor since the parallel relay also reverses and thereby connects the servo so that the motor continues to drive in a single direction. This type of arrangement performs the desired function but has the need of doubly switching the servo motor under certain conditions and this is not desirable. This system also requires that the relay be built directly into the servo control panel and provides no flexibility in the system. A system of the type generally described has been on sale by the assignee of the present invention and is known as the R7096A conveyor control system. The present invention is an improvement of this type of system wherein the shortest-route feature no longer reverses the sense of servo, but takes over control of the bridge that drives the motor so that the motor is never caused to reverse once it starts. This improved invention also allows for the provision of the override control as an auxiliary unit that can be sold or connected to the system when the purchaser desires this particular function, as opposed to a conveyor control system that balances in a normal fashion, that is, one which may not take the shortest route.

It is a primary object of the present invention to disclose a rebalance bridge servo control system with the added function of an override control that takes control of the system at a predetermined point from the normal bridge balance to operate the system and then return control to the bridge to finish its complete cycle.

A further object of the present invention is to provide a servo control system that senses an unbalance at a predetermined unbalance and switches a voltage into the bridge to override the bridge until the bridge is near balance before the voltage is removed.

Still a further object of the present invention is to disclosed a call office conveyor control system that utilizes an override control so that the conveyor operates in the shortest route even though the system normallywould have moved in the opposite or longest direction.

Yet another object of the present invention is to disclose a call ofiice conveyor system that can have a shortest-route function plugged into the system after the system is installed to convert a conventional conveyor system to the shortest-route type of system. I Still a further object of the present invention is to disclose a bridge balance system that is overridden by a voltage being applied to the bridge under a first predetermined condition, and having the voltage removed to restore the bridge to control when a second predetermined condition exists.

These and-other objects will become apparent when the drawings are considered with the present specification, wherein:

FIGURE 1 is a schematic top view of a conventional conveyor control with manual control operation;

FIGURE 2 is a top schematic view of a conveyor system incorporating the present override control in a plugin arrangement;

FIGURE 3 is a schematic representation of the entire control system applicable to FIGURE 2; and,

\ FIGURE 4 is a circuit diagram of the override control section of the system of FIGURE 3.

In FIGURE 1, a schematic top view of a conveyor is disclosed. The conveyor has a pulley or drive mechanism and a second support or idler pulley 11. The drive mechanism 10 and idler 11 are connected by a belt or chain 12 that form a hanging media for any number of garments or materials. In the particular system described, that is, a call ofiice conveyor system, the chain 12 would be broken up into a number of segments, each of which would be assigned a number. The number would then be jotted on a receipt corresponding to any garment hung on that particular location and this receipt would be placed at the cash register so that the operator of the system could pick off a garment when the appropriate number appeared. For convenience in considering the overall invention, it would be easiest to consider the chain 12 as broken up into 360 positions, one position for each degree of rotation of a circular member.

The pulley 10 is mechanically linked at 13 to a re versible motor 14* that is powered from any convenient electrical source. A control cable 15 passes to a customer counter control 16. The customer counter control 16, in this simple system, is nothing but a single pole, double throw switch so that the motor 14 can be controlled through cable 15 to operate in either direction. These directions will be referred as clockwise and counterclockwise with corresponding reference to the conveyor 12.

Upon the entry of a customer to a dry cleaning establishment and the presentation of identification in the form of name or receipt, the operator of the system notes the location of the desired garment on the conveyor system. If, for example, the desired garment is at point 17 on the conveyor belt 12, the operator at the customer counter control 16 would desire to have the system operate in a counterclockwise direction to deliver the point 17 to the customer counter control 16 with the conveyor traveling the shortest route. It is obvious that the operator at the customer counter control. 16 can make a determination of the shortest route by noting the position of the overall conveyor and the location of point 17, or by noting the number on the conveyor that is at the customer counter control 16 and the diiference from the desired number or location 17. The system of FIGURE 1 is the most basic and incorporates a simple manual control system.

In FIGURE 2, a top view similar to FIGURE 1 isdisclosed with additional control equipment. The conveyor has been numbered with identical numbers corresponding in the present disclosure.

to identical parts. It will be noted that, in additionto the system disclosed in FIGURE 1, a mechanical coupling 20 has been provided to drive a round-and-round potentiometer 21. The round-and-round potentiometer is connected by cable 22 to a second round-and-round potentiometer 23. The second round-and-round potentiometer 23 is incorporated in the customer counter control 16.

The round-and-round potentiometer 23 along with the round-and-round potentiometer 21 form the movable elements of a network normally referred to as a bridge network, which will be described in detail later in the present disclosure. The simple bridge network disclosed thus far is well known in the art, and by adjusting the potentiometer 23, it is possible to obtain an unbalance in the bridge which in turn activates the motor 14 to drive through the linkage 13 to drive the conveyor wheel or pulley 10. When the pulley 10 rotates the linkage 20 rotates to drive the potentiometer 21 thereby rebalancing the system. When the system rebalances, the motor 14 turns off and the conveyorbelt 12 comes to a stop. The system described so far is a conventional servo rebalance bridge type motor control and forms no immediate part of the novelty of the present invention. It has merely been disclosed as the type of system to which the novel invention is applied. The novelty of the present invention is in the plug-in override control unit and the means in which it operates. This unit will be described in detail The override control is disclosed at 25 connected by a cable 26 and a plug-in unit 27 to the potentiometer 23. The override control 25, cable 26, and connector or plug-in 27 form a unit which can be connected to a bridge system to add the shortestroute feature and also to add it in a fashion which is unique.

In FIGURE 3, a schematic representation of the overall control system, including the plug-in override control, has been disclosed. This system will be described in some detail and the numerical notations will correspond as far as practicable to the disclosures of FIG- URES 1 and 2. A round-and-round potentiometer 21 is provided which has a wiper 30 that is capable of being rotated continuously through 360". The potentiometer 21 can be considered a circuit element whose electrical characteristic is a unidirectional function of the position of the wiper 30 throughout a complete range of movement of the wiper 30 and which has a discontinuous transition between the ends 31 and 32 of the potentiometer 21. The wiper 30 is driven by mechanical connection 20 from the bidirectional or reversible motor 14. The reversible motor 14 is energized from any convenient source by a common conductor 33 along with the alternate conductors 34 and 35. The conductors 34 and 35 are connected to the power source by conductor 36 through relay contacts 38"or 40. The relay contacts 38 and 40 are selectively energized in response to the position of the wiper 30 of potentiometer 21 in a means that will be described separately.

The second potentiometer 23 has a freely movable wiper 41 and a pair of connections 42 and 43 at the ends of the active section of the potentiometer 23. The wiper 41 is freely movable in a manual fashion at the customer control counter 16 in order to set an unbalance into the bridge circuit of the present device. It will be noted that the ends 32 and 42 are connected by conductor 44, while the ends 31 and 43 are connected by conductor 45 to form two legs of a bridge circuit for the present unit. Appropriate power connections 46 and 47 are provided so that energy is conveyed to the bridge for its operation. The main output from the bridge is on conductors 50 and 51 which are in turn connected to the wipers 30 and 41 off the two potentiometers 21 and 23. The circuit thus described is a conventional round-and-rormd bridge balance circuit and is believed to require no further discussion as the elements are conventional.

The conductor 51 is also connected to a discriminator, amplifier, and power supply 52. The conductor 50 is connected to a fixed impedance or resistance 53 which is in turn connected by conductor 54 to the discriminator, amplifier, and power supply 52. The discriminator, amplifier, and power supply 52 are well known in the art and could be of a type disclosed in the B. H. Pinckaers Patent No. 2,911,545, issued in the United States on November 3, 1959. The Pinckaers patent fully discloses an equivalent circuit including the discriminator, amplifier, and power source for a similar type of operation. It is enough to know that the discriminator 52 is capable of sensing an unbalance of the bridge formed by the potentiometers 21 and 23 and selectively energizes a pair of relays 55 and 56. The relays 55 and 56 are energized depending on the phase of the input between conductors 51 and 54 to the discriminator and amplifier 52. The relay 55 has a contact 57 while relay 56 has a contact 58. The contacts 57 and 58 are respectively ganged to switches 38 and 40 so that the switches 57 and 38 operate as a unit while the switches 58 and 40 operate as a unit. The circuit through the relays 55 and 56 is completed on a conductor 60 that is powered from the discriminator and amplifier 52.

A second pair of switches 61 and 62 are provided with a ganging mechanism 63 so that the switches 61 and 62 operate as a single unit for momentarily shorting both the relays switches 57 and 58 to conductor 60. The ganging mechanism 63 is located at the customer counter control 16 and provides a momentary circuit to the relays 55 and 56 to start the system in operation.

The operation of a circuit disclosed in FIGURE} to this point will be briefly described. This is a basic bridge balance system and the novel override control that accompanies it has not been incorporated. The basic operation will first be described before the override control is detailed. The wiper 41 is manually positioned to correspond to a number on the conveyor 12 thereby setting an unbalance into the bridge that feeds the discriminator and amplifier 52. The discriminator and amplifier 52 immediately selects which of the relays 55 or 56 is to be energized, and upon pushing the ganging mechanism 63, the two relays are connected by conductor 60 to the appropriate power from the discriminator and amplifier 52. One of the relays 55 or 56 then pulls itself in and holds through the contacts 57 or 58. This immediately energizes the reversible motor 14 to drive in one direction or another thereby driving the wiper 30. The wiper 30 drives the system until the wiper 30 corresponds in position with wiper 41 thereby rebalancing the bridge. As soon as the discriminator and amplifier 52 sense the balance of the bridge, the power to the relay 55 or 56 is removed thereby opening the relay and disconnecting the motor 14 from power. This stops the drive of the conveyor 12 and the appropriate location on the conveyor has been brought to the customer counter control 16. With this arrangement, it is possible to obtain a remote control of the conveyor.

The system described to this point has one major drawback. The bridge formed of the potentiometers 21 and 23 will not balance by driving the wiper 30 over the discontinuity between ends 31 and 32 of the potentiometer 21. As such, whenever the system just described is energized, the motor is always activated to drive the potentiometer wiper 30 in a direction that will not require the wiper 30 to cross the discontinuity between 31 and 32. With the arrangement, it is possible thus to obtain a conveyor control that will remotely balance, but will not necessarily rebalance taking the shortest route of the conveyor 12 to the customer counter control 16. The present invention is directed to an add-on or plug-in unit which will accomplish this function in a new and unusual manner.

It will be noted that the system just described has a resistor or fixed impedance 53 in series with the wiper 30 between it and the discriminator 52. This resistance provides no signal that the discriminator and amplifier 52 of itself can sense since the resistor 53 is outside the input circuit between the conductors 51 and 54. The resistor 53 provides a function for the override control 25 that will now be described. Connected across resistor 53 are a pair of conductors and 71 that go to the connector 27, previously described. Connected to conductor 51 is a conductor 72 that also goes to the connector 27. Connector 27 has an extension of these three conductors cabled together at 73 and the cable 73 passes on to the override control 25. The override control is also powered from any convenient source.

The override control 25 provides two basic functions. The first function is a sensing of the bridge balance, and the second function is the addition of a voltage to the bridge unbalance whenever a predetermined condition exists. The operation will be briefly described with reference to the block diagram of FIGURE 3 in order to establish the function before the specifics of this circuitry are discussed. The override control 25 senses the degree of unbalance of the bridge formed by potentiometers 21 and 23 between the conductors 70 and 72, which is the input to the discriminator and amplifier 52. The override control 25 ignores any unbalance which is less than 50% of the voltage applied to the bridge on conductors 46 and 47. Any voltage unbalance of the bridge between the conductors 70 and 72 which is less than 50% of the voltage supplied to the bridge between conductors 46 and 47 indicates that the bridge is unbalanced in such a fashion that the motor 14 will normally drive the conveyor in its shortest direction to rebalance the system. Any voltage appearing between the conductors 70 and 72 which exceeds 50% of the bridge voltage appearing between 46 and 47 indicates that the appropriate direction for balance is to drive the wiper 30 across the discontinuity 31 and 32.

'Since the basic system is not normally capable of operating in this fashion, the override control 25 then switches a voltage on conductors 70 and 71 across the resistance 53 which is large enough and which is of the proper phase to completely override the signal from the bridge formed of the potentiometers 21 and 23 and which is in a phase to drive the motor 14 in a direction which will cause the wiper 30 to cross the discontinuity 31 and 32. Since the voltage supplied to the discriminator and amplifier 52 is a false signal voltage across the resistance 53, the voltage from the bridge supplied on conductors 50 and 51 has no effect on the direction of operation of the reversible motor. Upon the override control 25 sensing an unbalance in excess of the 50% of the power supply to the bridge, the reversible motor starts upon activating the ganging mechanism 63 to switches 61 and 62 to cause the motor to drive potentiometer wiper 30 in a direction to cross the discontinuity 31 and 32. As soon as the wiper 30 passes over the discontinuity of the open at 31 and 32, the bridge provides a signal that is less than 50% of the predetermined level of the applied voltage to the bridge. This then provides a signal between conductors 70 and 72 to the override control 25 that removes the voltage applied between conductors 7t) and 71 to the resistor 53. Upon removal of the voltage across 53 at the level of unbalance below the predetermined 50% point, the discriminator and amplifier 52 is put back under the control of the unbalance of the bridge formed by the potentiometers 21 and 23. The motor then is driving in the correct direction to complete the balance by the Wiper 30 of the potentiometer 21 thereby balancing the bridge and causing the system to have the conveyor drive across the discontinuity 31 and 32. This causes the system always to balance in a direction that is the shortest route.

It becomes obvious that by sensing the 50% point, and providing a false signal to the bridge discriminator and amplifier 52, it is always possible to cause the prescal circuit will be noted.

ent system to rebalance by operating in a shortest direction as far as the loop of the conveyor is concerned. It will also be noted that the plug 27 can be removed thereby removing the override control 25 without disturbing the basic bridge system. As such, the over-all control 25 can be added to the bridge system as a plug-in or addon unit to convert a system that does not take the shortest route to one which does take the shortest route. It is the heart of the present invention to provide a servo bridge balance type unit that has the add-on, plug-in feature of causing the system always to balance by causing the wiper, that is driven by the reversible motor, to move the shortest number of rotational degrees to accomplish balance. While systems of this general type are old, they have in the past utilized the concept of bypassing the discriminator and amplifier 52 with a signal rather than by controlling the discriminator-amplifier in preference to the control supplied vby the normal bridge. With the present inventions arrangement, it is possible to provide a plug-in unit separable at the plug 27, so that the conversion from one type of system to another can be readily made without any modification of the old or existing system. The details of the override control 25 will be described specifically in connection with FIGURE 4.

The override control circuit 25 has an input transformer 80 energized from any convenient source. The output of transformer 80 is a conventional pair of halfwave rectifier power circuits connected to capacitors 81 and 82 to provide two separate and independent direct current potential sources of the polarities marked. The voltage appearing across capacitor 81 is connected to a voltage divider formed of resistors 83 and 84 by conductors '85 and 86. Also connected across the conductors 85 and 86 is a second series network formed of a resistance 87 connected to an adjusting potentiometer 88, a capacitor 89, a second adjusting potentiometer 90, and a fixed resistance 91. Connected across the capacitor 89 is .a series network of a resistor 92, a diode 93, a diode 94, and a resistance 95. This last-named network has a conductor 96 connected to it between the diodes 93 and 94, and conductor 96 forms part of the previously-mentioned cable 73. The function of this particular conductor will be described in more detail sub sequently.

Also connected between the conductors 85 and 86 is part of a switching network including resistor 100 connected to transistor 101, which in turn is connected to the transistor 102 and then is connected to a resistor 103 that joins back to conductor 85. The transistors 101 and 102 are each in turn connected by conductors 104 and 105 across the capacitor 89 and its associated network of resistors and diodes. The circuit elements described to this point provide the primary or input circuits for means to the switching transistors 101 and 102 '113 and 114 to an intermediate conductor 115 which forms the third wire of the cable 73. It should be noted that for the most part, the values of the components recited are substantially equal in nature so that the two halves of the device appearing in the circuit are substantially symmetrical, with certain minor exceptions. In order to appreciate the general symmetry of the arrangements of components, the specific values for a typi- It should be understood that this is merly one successful embodiment of the circuit and forms no limitation on the circuit as it may be claimed and used. Typical values are as follows:

Circuit: Values Resistors 83 and 84 ohrns 1K Resistors 87 and 91 do 15K Potentiometers 88 and 90 do 10K Resistors 92 and d0 10K Diodes 93 and 94 1N9O Capacitor 89 ,u.f 0.33 Resistors and 103 -ohms 8.2K Transistors 101 and 111 2N1305 Transistors 10-2 and 112 2N1304 Diodes 113 and 114 1N645 Resistors 106 and 107 ohms 422 Voltage across capactitor 81 volts 12 Voltage across capacitor 82 do 18 As can be seen from the table of values, the circuit basically is symmetrical in configuration and for the most part forms a pair of balanced networks. The input to the present system occurs between conductors 96 and 115, while the output of the present circuit is between the conductor and conductor 115. In corresponding the circuits of FIGURES 3 and 4 it should be noted that conductor 96 joins at connector 27 with conductor 72, conductor connects at the connector 27 with conductor 70, and conductor 110 connects at the connector 27 with conductor 71.

A brief description of the operation of FIGURE 4 will point up how this circuit both senses the unbalance of the bridge and then, if necessary, overrides the control of the bridge to the discriminator and amplifier 52. The conductors 96 and 115 are connected to sense across the input to the discriminator and amplifier 52 and at a quiescent condition when no signal occurs between the conductors 96 and 115, the transistors 101 and 102 are both biased in an on condition. These two halves of the circuit are adjusted to be equal to one another by adjusting the potentiometers 88 and 90. Each of the transistors 101 and 102 draws equal currents from the voltage source across capacitor 81 through their associated resistors 87, 88, 90, and 91 along with the voltage divider resistors 83 and 84. Thus, in a quiescent condition, the current flow from the positive terminal of the capacitor 81 passes up through resistor 84 along conductor 115, through transistor 101 and passes through the resistances 88 and 87 to the negative side of the potential at 81. A current path from the positive side of 81 through resistor 91, 90 and the transistor 102 through conductor 115 and then up through resistor 83 back to the negative side of 81 occurs. These two current flows, at a quiescent condition, are adjusted to be equal and opposite and both of the transistors 101 and 102 are on. When the transistors 101 and 102 are drawing their equal and opposite current, the voltage applied to transistors 111 and 112 is such that it biases both of these transistors to a full off condition. As such, the voltages appearing across resistors 106 and 107 are equal and the output on conductors 110 and 115 is zero.

If the unbalance of the bridge to which the present circuit is connected rises beyond a value equal to one-half of the bridge voltage, the voltage rise appears across the conductors 115 and 96. This voltage causes a current flow equal and opposite to the quiescent current flow through one of the transistors 101 and 102. When the current fiow through one of the transistors 101 or 102 reaches a point to turn the transistor off, the circuit switches by feeding back through the input impedance of the discriminator-amplifier 52 and the associated one or the other of the transistors 111 or 112 switches on. When the associated transistor 111 or 112 switches on, it in effect places a short across part of the voltage divider formed of resistors 106 and 107 thereby upsetting the equal and opposite balance of voltages appearing across this voltage divider network. This immediately switches a definite voltage between the conductors 115 and 110. These conductors supply the voltage directly across the resist-or 53 (FIGURE 3), thereby biasing the discriminator and amplifier 52 in such a manner as to reverse its normal operation and overcome the bridge signal so that the operation for the circuit of FIGURE 3 occurs.

In very general terms, the input to the circuit of FIG- URE 4 turns ofif either transistor 101 or 102 which in turn turns on the transistor 111 or 112 associated with it. When either transistor 111 or 112 is on, the voltage divider made up by resistors 106 and 107 shifts to apply this unbalance of voltage across the resistance 53 to control the discriminator and amplifier 52.

If it is assumed that transistor 102 has been switched off and transistor 112 has been turned on, a resistance of approximately 1,000 ohms (the resistance of resistor 53) is placed in parallel with resistor 107 and this parallel combination in efiect is connected in series with resistance 106. This combination thus applies a shift in voltage between the output conductors 110 and 115 so that the circuit of FIGURE 4 controls the discriminator and amplifier S2 to drive the wiper 30 across the open between 31 and 32. As the bridge network approaches a balance condition, this is sensed between the conductors 96 and 115. When the condition of the predetermined voltage (less any operating differential) occurs, the transistors 101 and 102 sense a change in current flow. When the current flow due to an unbalance on conductors 96 and 115 drops to a sufficient point, the transistors 101 and 102 take over their normal quiescent flow function thereby turning off the transistor 111 or 112, whichever has been on, and restores the system so that no output exists on conductors 110 and 115 to the resistor 53. Under these conditions, the bridge takes over control of the discriminator and amplifier 52 and the circuit of FIGURE 4 merely becomes passive awaiting an unbalance in excess of 50% of the bridge supply voltage once again.

With the arrangement just disclosed, a system for sensing the unbalance of a bridge is provided wherein, when ever a predetermined unbalance exists, the system switches in a false voltage to the bridge thereby taking control of the servo system that the bridge normally operates, away 'from the bridge and placing it under the control of the fixed applied voltage. When the bridge unbalance is restored to a level below the predetermined control point, the circuit of FIGURE 4 removes itself from control of the discriminator-amplifier 52 and gives the control back to the normal bridge functions. With this arrangement, the sensing and control occurs whenever an excess voltage appears across the bridge indicating that the direction of rebalance would be shortest if the system operated to drive the wiper 30 across the discontinuity between connections 31 and 32 of the potentiometer 21. With this arrangement, a shortest-route feature is added to an otherwise normal bridge balance circuit and this addition can be accomplished by merely adding a plug-in unit having three conductors going to the bridge balance system. It is thus apparent that a unique means of adding a control system to a bridge has been provided and that the means of controlling the bridge, once that control becomes necessary, is unique in that the control is taken away from the normal bridge balance elements and is given to the override control until the need for the override control is removed. Since the circuit of FIGURE 4 can be replaced by many dilferent types of circuits, even circuits including conventional relay switching devices, it becomes obvious that many modifications of the present invention are possible. The modifications would be obvious to one skilled in the art and only one embodiment has been disclosed. The applicants wish to be limited in the scope of their invention only by the scope of the appended claims.

We claim as our invention:

1. In a closed loop conveyor system, including: a bidirectional motor driven continuous closed loop conveyor having a call station; a pair of variable circuit elements each having an electrical characteristic that is a unidirectional function of the position of .a control member throughout a range of movement and having a discontinuous transition upon rep-eating l8, cycle of movement; bridge network means capable of being balanced and including said pair of variable circuit elements and 'a fixed resistor; a first of said circuit elements mounted upon said conveyor and having its electrical characteristic vary as said conveyor is driven by said motor so that a complete cycle of said electrical characteristic occurs for each complete cycle of said conveyor past said call station; the other of said circuit elements having a control member freely movable at said call station to unbalance said bridge network means by an amount corresponding to a position of said conveyor system; servo means including said motor responsive to Ian unbalance of said bridge network means and adapted to move the first of the control members in such a sense as to restore said network means to a balanced condition; override control means connected to said bridge network means to sense and control the unbalance of said network means; said override control means including a pair of balanced transistor input switching circuits connected to said network means to sense the degree of unbalance of said bridge network means and at least one of said circuits switching at a predetermined amount of unbalance of said network means; said override control means further including .a pair of transistor output switching circuits connected to said resistor and controlled by said input switching transistor circuits; and said output switching circuits applying a voltage source to said resistor when the degree of unbalance is above said predetermined amount to control said servo means by overriding said .bridge network means unbalance; said override control means further restoring control to said bridge network means and said servo means when the network unbalance is less than said predetermined amount by said output switching transistors removing said voltage source -from said bridge network means.

.2. In a closed loop conveyor system, including: a bidirectional motor driven continuous closed loop conveyor having a call station; a pair of variable circuit elements each having an electrical characteristic that is a unidirectional function of the position of a control member throughout a range of movement and having )Et discontinuous transition upon repeating a cycle of movement; bridge network means capable of being balanced and including said pair of variable circuit elements and an impedance; l3. first of said circuit elements mounted upon said convey-or and having its electrical characteristic vary as said conveyor is driven by said motor so that -a complete cycle of said electrical characteristic occurs for each complete cycle of said conveyor past said call station; the other of said circuit elements having a control member freely movable at said call station to unbalance said network means; servo means including said motor responsive to an unbalance of said net-work means and adapted to move the first of the control members in such a sense as to restore said bridge network means to a balanced condition; override control means connected to said network means to sense and control the unbalance of said network means; said override control means including input switching means in circuit with said network means to sense the degree of unbalance of said network means and to switch at a predetermined amount of unbalance of said bridge network means; said override control means further including output switching means connected to said impedance and controlled by said input switching means; and said output switching means applying voltage source means to said impedance when the degree of unbalance is above said predetermined amount to control said servo means; said override control means further restoring control to said network means and said servo means when the network unbalance is less than said predetermined amount by said output switching means removing said voltage source means from said impedance.

3. In a closed loop conveyor system, including: a bidirectional motor driven continuous closed loop conveyor having a call station; a pair of variable circuit elements at least one of which has an electrical characteristic that is a unidirectional function of the position of a single control member throughout a range of movement and having a discontinuous transition upon repeating a cycle of movement; network means capable of being balanced and including said pair of variable circuit elements; a first of said circuit elements including said single control member mounted upon said conveyor with said first circuit element having its electrical characteristic vary as said conveyor is driven by said motor so that a complete cycle of .said electrical characteristic occurs for each complete cycle of said convevor past said call station; the other of said circuit elements having a control member freely movable at said call station to unbalance said network means; servo means including said motor responsive to an unbalance of said network means and adapted to miove the of the control members in such a sense as to restore said network means to a balanced condition; and override control means connect-ed to said network means to sense and control the unbalance of said network means; said override control means overriding said network means by applying a potential to said network means to control said servo means whenever the network unbalance exceeds a servo means responsive to an unbalance of said bridge network means and adapted to move said control means in such a sense as to restore-said bridge network means to a balanced condition; override control means connected to said bridge network means to sense and control the unbalance of said network means; said override control means including a pair IO'f balanced transistor input switching circuits connected to said network means to sense the degree of unbalance of said bridge network means and at least one of said circuits switching at a predetermined amount of unbalance of said network means; said override control means further including a pair'iof transistor output switching circuits connected to said resistor and controlled by said input switching transistor circuits; and said output switching circuits applying a voltage source to said resistor when the degree of unbalance is above said predetermined amlount to control said servo means by overriding said bridge network means unbalance; said override control means further restoring control to said bridge net-work means and said servo means when the network unb alanoe is less than said predetermined amount by said output switching transistors removing said voltage source from said bridge network means.

5. In a rebalance servo control system, including: variable circuit element means whose electrical characteristic is a unidirectional function of the position of .control means throughout a range of movement and has a discontinuous transition upon repeating a cycle of movement; network means capable of being balanced and including said variable circuit element means; said network means further including an impedance; servo means responsive to an unbalance of said network means and adapted to move said control means in such a sense as to restore said network means to a balanced condition; override control means connected to said network means to sense and control the unbalance of said network means; said override control means including input switching means in circuit with said network means to sense the degree of unbalance of said network means and to switch at a predetermined amount of unbalance of said network means; said override control means further including output switching means connected to said impedance and controlled-by said input switching means; and said output switching means applying voltage source means to said impedance when the degree of unbalance is above said predetermined amount to control said servo means; said override control means further restoring control to said network means and said servo means when the network unbalance is less than said predetermined amount by said output switching means removing said voltage source means from said impedance.

6. In a rebalance servo control system, including: a

pair of potentiometers each having an electrical resistance that is a unidirectional function of the position of a control wiper throughout a range of movement and having a discontinuous transition upon repeating a cycle of movement; a bridge network means capable of being balanced and including said otentiometers; said bridge network means further including a fixed resistance in an output leg thereof; a first of said wipers being manually adjustable to unbalance said bridge network means; servo means responsive to an unbalance of said bridge network means and adapted to move the other of the wipers in such a sense as to restore said bridge network means to a balanced condition; and override control means connected to said bridge network means to sense and control the unbalance of said network means; said override control means overriding said network means by applying a voltage to said fixed resistance to control said servo means whenever the bridge network unbalance exceeds a predetermined first amount; said override control means removing said voltage thereby restoring control to said bridge network means and said servo means when the network unbalance is less than a second predetermined amount.

7. In a rebalance servo control system, including: a pair of variable circuit elements each having an electrical characteristic that is a undirectional function of the position of a control member throughout a range of movement and having a discontinuous transition upon repeating a cycle of movement; network means capable of being balanced and including said pair of variable circuit elements; said network means further including a fixed impedance; a first of said control members being freely movable to unbalance said network means; servo means responsive to an unbalance of said network means and adapted to move the other of the control members in such a sense as to restore said network means to a balanced condition; and override control means connected to said network means to sense and control the unbalance of said network means; said override control means overriding said network means by applying a potential to said fixed impedance to control said servo means whenever the network unbalance exceeds a predetermined amount; said override control means removing said potential thereby restoring control to said network means and said servo means when the network unbalance is less than said predetermined amount.

8. In a rebalance servo control system, including: a variable circuit element whose electrical characteristic is a unidirectional function of the position of a control member throughout a range of movement and has a discontinuous transition upon repeating a cycle of move- .ment; network means capable of being balanced and including said variable circuit element; said network means further including a fixed impedance; servo means responsive to an unbalance of said network means and adapted to move said control member in such a sense as to restore said network means to a balanced condition; and override control means connected to said network means to sense and control the unbalance of said network means; said override control means overriding said network means by applying a potential to said fixed impedance to control said servo means whenever the network unbalance exceeds a predetermined amount; said override control means removing said potential thereby restoring control to said network means and said ser-vo means when the network unbalance is less than said predetermined amount.

9. In a rebalance servo control system, including: variable circuit element means whose electrical characteristic is a unidirectional function of the position of control means having a single wiper element throughout a range of movement and has a discontinuous transition upon repeating a cycle of movement; network means capable of being balanced and including said variable circuit element means; ser-vo means responsive to an unbalance of said network means and adapted to move said single wiper element relative to the balance of said control means in such a sense as to restore said network means to a balanced condition; and override control means connected to said network means to sense and control the unbalance of said network means; said override control means overriding said network means to control said servo means whenever the network unbalance exceeds a predetermined amount; said override control means further restoring control to said network means and said servo means when the network unbalance is less than said predetermined amount.

References Cited by the Examiner UNITED STATES PATENTS 2,384,622 9/45 Isserstedt 318--29 2,786,169 3/57 Mufily 31829 2,861,233 11/58 McKeown 318--29 3,155,889 11/64 Stiles et a1. 31829 X JOHN F. COUCH, Primary Examiner. 

1. IN A CLOSED LOOP CONVEYOR SYSTEM, INCLUDING; A BIDIRECTIONAL MOTOR DRIVEN CONTINUOUS CLOSED LOOP CONVEYOR HAVING A CALL STATION; A PAIR OF VARIABLE CIRCUIT ELEMENTS EACH HAVING AN ELECTICAL CHARACTERISTIC THAT IS A UNDIRECTIONAL FUNCTION OF THE POSITION OF A CONTROL MEMBER THROUGHOUT A RANGE OF MOVEMENT AND HAVING A DISCONTINUOUS TRANSITION UPON REPEATING A CYCLE OF MOVEMENT; BRIDGE NETWORK MEANS CAPABLE OF BEING BALANCED AND INCLUDING SAID PAIR OF VARIABLE CIRCUIT ELEMENTS AND A FIXED RESISTOR; A FIRST OF SAID CIRCUIT ELEMENTS AND A FIXED CONVEYOR AND HAVING ITS ELECTRICAL CHARACTERISTIC VARY AS SAID CONVEYOR IS DRIVEN BY SAID MOTOR SO THAT A COMPLETE CYCLE OF SAID ELECTRICAL CHARACTERISTIC OCCURS FOR ECH COMPLETE CYCLE OF SAID CONVEYOR PAST SAID CALL STATION; THE OTHER OF SAID CIRCUIT ELEMENTS HAVING A CONTROL MEMBER FREELY MOVABLE AT SAID CALL STATION TO UNBLANCE SAID BRIDGE NETWORK MEANS BY AN AMOUNT CORRESPONDING TO A POSITION OF SAID CONVEYOR SYSTEM; SERVO MEANS INCLUDING SAID MOTOR RESPONSIVE TO AN UBALANCE OF SAID BRIDGE NETWORK MEANS AND ADAPTED TO MOVE THE FIRST OF THE CONTROL MEMBERS IN SUCH A SENSE AS TO RESTORE SAID NETWORK MEANS TO A BALANCED CONDUITION; OVERRIDE CONTROL MEANS CONNECTED TO SAID BRIDGE NETWORK MEANS TO SENSE AND CONTROL THE UNBALANCE OF SAID NETWORK MEANS; SAID OVERRIDE CONTROL MEANS INCLUDING A PAIR OF BALANCED TRANSISTOR INPUT SWITCHING CIRCUITS CONNECTED TO SAID NETWORK MEANS TO SENSE THE DEGREE OF UNBALANCE OF SAID NETWORK AND MEANS TO SENSE THE LEAST ONE OF SAID CIRCUITS SWITCHING AT A PREDETERMINED AMOUNT OF UNBALANCE OF SAID NETWORK MEANS; SAID OVERRIDE CONTROL MEANS FURTHER INCLUDING A PAIR OF TRANSISTOR OUTPUT SWITCHING CIRCUITS CONNECTED TO SAID RESISTOR AND CONTROLLED BY SAID INPUT SWITCHING TRANSISTOR CIRCUITS; AND SAID OUTPUT SWITHING CIRCUITS APPLYING A VOLTAGE SOURCE TO SAID RESISTOR WHEN THE DEGREE OF UNBALANCE IS MOVE SAID PREDETERMINED AMOUNT TO CONTROL SAID SERVO MEANS BY OVERRIDING SAID BRIDGE NETWORK MEANS UNBALANCE; SAID OVERRIDE CONTROL MEANS FURTHER RESTORING CONTROL TO SAID BRIDGE NETWORK MEANS AND SAID SERVO MEANS WHEN THE NETWORK UNBALANCE IS LESS THAN SAID PREDETERMINED AMOUNT BY SAID OUTPUT SWITCHING TRANSISTORS REMOVING SAID VOLTAGE SOURCE FROM SAID BRIDGE NETWORK MEANS. 